The system was introduced by the US military but today anyone can access its services through the use of a GPS receiver (McNamara, 52).
The satellite system uses a trilateration principle to determine the location of the receiver (Maini and Varsha, 428). In three dimension trilateration, the requirement for the system to generate the exact location of the receiver is a direct line of signal from at least three satellites and the distance between a receiver and the satellites (Maini and Varsha, 411). These details are obtained by the receiver from analyzing the high frequency radio signals from the satellites. This distance is derived from a calculation of the time used by the frequencies to travel from one satellite to the receiver on a location that is on earth. This measurement is only possible if the time in both the satellite and the receiver are synchronized.
Otherwise the delay would not give an accurate value of the distances obtained. To synchronize the time in space and the time in the atmosphere where gravity pulls are varied requires both the receiver and the satellite to have atomic clocks. However atomic clocks are very expensive and as such, the GPS system uses an error correction method that involves the fourth satellite. From the fourth satellites transmission of signals, the inaccuracy in trilatration is appropriately adjusted (Maini and Varsha, 308). The calculation for the error adjustment by the receiver is repeated several times to make the receiver just as effective without the atomic watch for synchronization.
Further errors are bound to arise in the process of calculating the distance and location of the receiver. These include the effect of delays of signals in different layers of the atmosphere. However, the speed of electromagnetic waves is not affected and travels at the same speed as that of light. In different substances, the speed is considerably reduced. These variations in the speed of the waves are